Despite the large number of on-going research studies in the field of various electro-chromic (EC) technologies, there is still a need of compact and mechanically-robust solid-state electro-chromic film stack, which can be easily applied on an existing lens blank, semi-finished blank (SFB) or other surfaces that need controllable variable transmission performance. Such an EC stack should operate under low voltage, and thus, not require large, heavy and aesthetically non-acceptable batteries. Furthermore, the variable transmission EC stack should be fast-responding with a satisfactory dynamic range compared to the current available photochromic lenses and other switching technologies.